Uniaxial Swelling in LC Hydrogels Formed by Two-Step Cross-Linking

Abstract

Molecularly oriented hydrogels of sacran, which is a supergiant liquid crystalline polysaccharide extracted from Aphanothece sacrum biomaterials, showing ultrahigh anisotropy of swelling is successfully prepared by two-step chemical crosslinking. Divinyl sulfone (DVS) works as a chemical cross-linker of sacran chains in a dilute aqueous solution to form hydrogels, but some of the added DVS remains in the hydrogel without cross-linking. The remaining DVS cross-links further with the preformed networks of sacran chains in liquid crystalline state during slow drying to produce in-plane oriented xerogels. The xerogels show heterogeneous anisotropy in the successive swellings steps; the linear swelling ratio in the thickness direction is 10000−40000-fold higher than that in the width direction due to the molecular orientation of the sacran hydrogels. X-ray diffraction imaging of the hydrogels reveal not only the orientation of the xerogel films but also the unusual orientation of water molecules binding to sacran networks in the hydrogel state.

Covalently Cross-Linked and Mechanochemiluminescent Polyolefins Capable of Self-Healing and Self-Reporting

“…8,11 The cross-linking densities of HBM-Ad-COEUs were evaluated by swelling experiments. 30,31 With cross-linker Ad content increasing, the swelling ratio in CHCl 3 decreased, while the gel content increased instead (Supporting Information Figure S3). In addition, the good thermal stability of HBM-Ad-COEUs was supported by thermogravimetric analysis (TGA; Supporting Information Figure S4).…”

The Use of Megamolecular Polysaccharide Sacran in Food and Biomedical Applications

“…For instance, a helix transition concentration occurs when a chain of sacran changes from a random coil into a double helix at 0.09%, and gelation concentration occurs when sacran transitions from liquid to gel at 0.25% [ 28 , 29 ]. With increasing concentration, the sacran chain changes into a rigid rod form, showing liquid crystalline (LC) properties [ 30 , 31 ]. Sacran can form a gel-like film that is difficult to re-dissolve in water.…”

The cyanobacterial polysaccharide sacran: characteristics, structures, and preparation of LC gels

“…Focusing on the liquid crystallinity, LC gels were prepared by introducing physical or chemical cross-linking points [23,24,27,29]. Specifically, in-plane-oriented films were obtained by drying the LC aqueous solutions at a temperature of 60°C.…”

“…The micropores were apparently interconnected during the process, similar to tunnels in the internal structure of the hydrogels [35]. On the other hand, chemically cross-linked gels with layered structures were also prepared by using divinyl sulfone among carboxyl groups in sacran chain [24]. Thus, the LC characteristics of sacran allowed the preparation of a Polarized microscopic image of sacran solution in a cell with a 1 mm gap after 6 h of drying at 60°C.…”